This invention generally relates to apparatus and methods of forming inkjet print head nozzle plates and more particularly relates to a mandrel for forming an inkjet print head nozzle plate having a non-wetting surface of uniform thickness and an orifice wall of tapered contour, and method of making the mandrel.
An ink jet printer produces images on a receiver by ejecting ink droplets onto the receiver in an imagewise fashion. The advantages of non-impact, low-noise, low energy use, and low cost operation in addition to the capability of the printer to print on plain paper are largely responsible for the wide acceptance of ink jet printers in the marketplace.
In one type of "drop on demand" ink jet printer, a print head formed of piezoelectric material includes a plurality of ink channels, each channel containing ink therein. In such a printer, each of these channels is defined by a pair of oppositely disposed sidewalls made of the piezoelectric material. Also, each of these channels terminates in a channel opening for exit of ink droplets onto a receiver disposed opposite the openings. The piezoelectric material possesses piezoelectric properties such that an electric field applied to a selected pair of the sidewalls produces a mechanical stress in the sidewalls. Thus, the pair of sidewalls inwardly deform as the mechanical stress is produced by the applied electric field. As the pair of sidewalls defining the channel inwardly deform, an ink droplet is squeezed from the channel. Some naturally occurring materials possessing such piezoelectric characteristics are quartz and tourmaline. The most commonly produced piezoelectric ceramics are lead zirconate titanate (PZT), barium titanate, lead titanate, and lead metaniobate. However, it is desirable that the ink droplet exiting the channel opening travels along a predetermined trajectory and that the droplet has a predetermined velocity and volume, so that the droplet lands on the receiver at a predetermined location to produce a pixel of a predetermined size.
Therefore, it is customary to attach a nozzle plate to the print head so that the ink droplet achieves the desired volume, velocity and trajectory. The nozzle plate has nozzle orifices therethrough aligned with respective ones of the channel openings. The purpose of the orifices is to produce ink droplets having the desired volume and velocity. Another purpose of the orifices is to direct each ink droplet along a trajectory normal (i.e., at a right angle) to the nozzle plate and thus normal to the receiver surface. To achieve these results, the diameter and interior contour of the nozzle orifices are controlled. If as-built diameter and/or interior contour of the nozzle orifice deviates from a desired diameter and contour, ink droplet trajectory, volume and velocity can vary from desired values. In other words, such a nozzle plate should ensure that the ink droplet exiting the channel opening will travel along the predetermined trajectory with the predetermined volume and velocity so that the droplet lands on the receiver at the predetermined location and produces a pixel of predetermined size. To accomplish this result, each orifice is preferably precisely dimensioned and internally contoured (e.g., tapered) as previously mentioned, so that each ink droplet exiting any of the orifices travels along the predetermined trajectory with predetermined volume and velocity. This result is important in order to avoid image artifacts, such as banding. Therefore, the technique used to make the nozzle plate should produce nozzle plate orifices that are precisely dimensioned and internally contoured to avoid such undesirable image artifacts.
Moreover, it is important that the exterior surface of the nozzle plate have a so-called "non-wetting" characteristic. That is, it is known that direction of ink droplet trajectory can deviate from a desired trajectory if the vicinity of the nozzle orifice becomes nonuniformly wet with ink. Furthermore, as the nozzle plate surface becomes increasingly wet with ink during use, the volume, velocity and trajectory characteristics of the ink drop can be affected. This results in an unintended variation in quality of the printed image. Additionally, an accumulation of ink on the nozzle plate surface may dry-out over a period of time. This affects the above-mentioned ink drop characteristics and may even cause blocking of the nozzle. Therefore, it is desirable that the vicinity of the nozzle orifice resist liquid ink accumulation. In addition, it is desirable that any non-wetting layer coated on the exterior surface of the nozzle plate have uniform thickness, so that the non-wetting characteristic is the same among nozzle orifices of a single nozzle plate.
Manufacturing processes for producing templates having irregularly shaped apertures are known. In this regard, a process for manufacture of templates is disclosed in U.S. Pat. No. 4,264,714 titled "Process For The Manufacture Of Precision Templates" issued Apr. 28, 1981 in the name of Guinter E. Trausch. The Trausch patent discloses a process for manufacture of precision flat parts utilizing a metallized glass carrier having a stencil etched thereon with a negative working photo resist laminated on the carrier. Exposure of the photo resist is achieved through the glass so that maximum intensity of light in the photo resist occurs at the junction between the photo resist and the glass carrier for maximum adhesion. The Trausch patent also discloses that irregularly shaped apertures can be generated by selective varied orientation of the glass carrier during the exposure. However, the Trausch patent does not disclose a process expressly for manufacturing a mandrel for forming an inkjet print head nozzle plate. Also, the Trausch patent does not disclose an inkjet print head nozzle plate having a non-wetting surface layer.
However, an inkjet nozzle plate having an ink-repellent coating layer is disclosed in U.S. Pat. No. 5,759,421 titled "Nozzle Plate For Ink Jet Printer And Method Of Manufacturing Said Nozzle Plate" issued Jun. 2, 1998 in the name of Kiyohiko Takemoto, et al. The Takemoto, et al. patent discloses that a nozzle plate is immersed into an electrolyte in which particles of a water-repellent high molecular resin are dispersed by electric charges to form an ink-repellent coating layer on the front surface of the nozzle plate. According to the Takemoto et al. patent, the ink-repellent coating layer is an eutectoid plating layer or a fluorine-containing high molecular water-repellent agent applied by sputtering or dipping. However, sputtering or dipping may not provide an ink-repellent coating having a uniform thickness. Thus, although the Takemoto et al. patent discloses a method of making a nozzle plate having an ink-repellent coating layer, the Takemoto et al. patent does not appear to disclose a method of making the nozzle plate such that the nozzle plate is ensured of having an ink-repellent coating layer of uniform thickness. In addition, it appears that if the ink-repellent coating layer of the Takemoto et al. patent is a polymer, then the layer may be prone to being abraded. Moreover, it appears the Takemoto et al. patent requires additional processing steps after the nozzle plate is formed, thereby increasing fabrication costs. It would therefore be desirable to avoid these increased fabrication costs by elimination such additional fabrication steps.
Therefore, there has been a long-felt need to provide a mandrel for forming a nozzle plate having a non-wetting surface of uniform thickness and an orifice wall of tapered contour, and method of making the mandrel.